Production of sound and other records



Jan. 20 1942. 4 c. M. BURRl LL PRODUCTION OF SOUND AND OTHER RECORDS Filed Dec. 24, 1957 m nm m m .1. Mann.

ZSnventor attorney a k N I N A W m wfl v m. y u a, me 7 a f 6 mm W 5% 2 fi Patented Jan. 20, 1942 UNITED STATES- PATENT OFFICE,

Charles M. Burrill, Haddonfield, N. J assignor to Radio Corporation of America, a corporation of Delaware Application December 24, 1937, Serial No. 181,635

11 Claims.

This invention relates to the production of sound and other records such as are adapted for use in conjunction with motion pictures, and has for its principal object the provision of an improved system and method of operation whereby the volume, frequency components or other characteristics of the reproduced sound may be automatically controlled more satisfactorily than heretofore.

Otherwise stated, the present invention involves the recording of a discontinuous control record which may be located between the sprocket holes or the picture frames of a motion picture film. Insofar as it contemplates the provision of a control track between thesprocket holes or picture frames, the invention is similar to the invention disclosed by my copending application, Seerial No. 181,634, filed Dec. 24, 1937, and assigned to the same assignee as the present application. The present invention, unlike that of the aforesaid application, does not involve utilization of the sprocket holes or frame lines to produce carrier impulses for the signal.

As Will hereinafter appear, the improved record in its preferred form involves a succession of tuned or spaced repetitions, th transparency of the record area corresponding to each of these repetitions being varied in accordance with the function which it is desired to control. If the record is aligned with the sprocket holes of a motion picture film, for example, the period of the repetitions isof course determined by the spacing of the sprocket holes and it is essential be used with an optical system of correspondingly reduced resolving power, just as simply andsatisfactorily as the older form of track, which we shall refer to as continuous. Such an optical system of decreased resolution may be used in connection with a control track located along the sprocket holes of ordinary moving picture film, as described in my aforesaid application. It is advantageous to decrease the resolution as much as possible and still obtain the desired performance, since this increases the sensitivity and emciency of the optical system. Thus, the discontinuous track is satisfactory and particularly suitable for the sprocket hole control track.

that the record periods or repetitions not only be made to accommodate the sprocket hole spacing but also that the repetitions be in phase or synchronous with these spacings.

In the usual photographic sound track, the blackened area is usually thought of as continuous. examination under a'high power microscope will show. Actually, the blackening is produced by a multitude of very small and largely separate silver grains. This sort of deposit appears continuous to the naked eye, because of the limited This, however, is not actually the case, as

An advantage of the discontinuous track in accordance with this invention is that it may be recorded with very simple apparatus, if desired without any mechanical moving parts such as are required in the usual variable area and variable density recording systems, and without the inconvenient use of liquid cells such as Kerr cells.

Another advantage of the discontinuous track is that periodic and synchronous irregularities in the film, such as sprocket holes, may be so located with respect to the discontinuities in the track that they have no harmful effect.

One method of producing a useful discontinuous track is as follows: First, a suitable repetition rate for the discontinuities must be selected. This rate must be fast as compared with the maximum rate of change of the intelligence to be recorded, and if interference from a certain periodic disturbance is to be eliminated, the repetition'frequency must be equal to, a multiple, or av sub-multiple of this disturbance frequency. In the case of a control track for volume expansion, for example, 60 cycles per second would be a suitable and convenient repetition rate,'or if the track is to be placed over the sprocket holes, interference from them will be avoided by using a repetition frequency equal to the sprocket hole frequency,96 cycles per second for standard 35 mm. motion picture film.

Then, the desired intelligence is recorded by varying in each repetition cycle, the time (or distance along the track) during which the track is uniformly black. One way of accomplishing this is to use an exciter lamp for the recording exposure fast enough in response to follow the repetition frequency, such as a glow discharge lamp, and then supply it :with the desired approximately rectangular constant amplitude wave of current,- at the repetition frequency and in proper phase. with a simple rotating commutator with an ad- Such a wave maybe easily generated B50 and 3100. Fig. 5 assumes a point contact but this cam may justabl brush to accomplish the desired variation or modulation.

The invention will be better understood from the following description considered in connection with the accompanying drawing and its scope is indicated by the appended claims.

Referring to the drawing,

Figure 1 is a section of sound motion picture film having a discontinuous record in alignment with its sprocket holes,

Figures 2, 3 and 4 are explanatory diagrams relating to the characteristic features ofthe discontinuous record,

Figure 5 illustrates one suitable type of recorder for producing the discontinuous record, and

Figure 6 is a wiring diagram of an apparatus adapted to reproduce a sound record under the control of the discontinuous record.

The sound motion picture film I of Fig. 1 ina cludes the usual sound record II and a discontinuous control record 42 which islocated between the-sprocket holes of the film.

As shown "by Fig. '2, the "discontinuous record i2 comprisesaseries 'o'f dashes of a length which varies in accordance with the effect to be produced. The beginnings 'of'ithese dashes are indicated at a1, on, as, etouand their ends are indicateda'tbi, b2, 223, etc. In Fi'g. 2, the beginnings of the dashes are illustrated as in constant phase, l/T being the repetition frequency and the dash ends being advanced in phase to produce modulation of the record.

Fig. 3 illustrates an alternative mode of operation wherein-the dash beginnings 'are retarded in phase simultaneously with advance in the phase of the dash endings.

Figure '4 illustrates the control-function represented by the modulation of "the discontinuous records of Figs. '2 -and3, the curve of this figure showing the control effect as a function of time or the length of the clashes of the record.

Thus, the ordinates representthe percentage f the periodic record "area which is opaque and the abscissae represent time as measured longitudinally of the record at the recording speed. Otherwise stated, the ordinates may be considered as'the-position of the brush of a cam switch recorder such as that of Fig. 5 and the abscissae may be considered as'the rotational speed of this recorder.

The cam switch recorder or commutator of Fig. '5 is suitable for controlling energization'of a glow discharge lamp or the like for producing the dashes of a discontinuous record such as Fig. 2. Obviously, a symmetrical cam could be similarly provided to 'produce a track such as Fig. 3. The cam switch consists of a disc, part conductor and part insulator as indicated on the drawing. Obviously, an n-lobed cam may be used if itbe rotated atl/n of the speed. The cam conductor forms one terminal of the switch and a brush movable along the line O-X forms the other'terminal. B0 indicates the position of the brush for zero modulation. Corresponding brush positions for 50 and 100% modulations are "indicated at The d'e'sign of the cam shown in be "easily modified for any given finite brush shape. Any suitable drive mechanism may be used to move the brush or a plurality of brushes may be used and the desired one selected by a switch,thus giving a step by step modulation.

The controltrackin accordance with this invention may be recorded on standard mm.

motion picture film, along the sprocket holes, without interference from the sprocket holes, although a negligible stray modulation will be produced in effect by the difference between the density of clear film and of hole. In order to do this, the repetition rate should be made the same as that of the sprocket holes, namely 96 cycles per second. Also the maximum modulation would then be limited to approximately since the sprocket hole occupies 42% of the sprocket hole pitch. Also the phase of the recording must be such as to place the dots on film and not on hole. This may be done by adjusting the angular position of the brush (line OX) of Fig. 5. It will, of course, be readily understood that, in the illustrated embodiment of the invention, the commutator of Fig. 5 makes one revolution per sprocket hole of the film and that the length of the dash between each pair of sprocket holes is determined by the position of the brush which may, obviously, be moved along the line OX either manually or automatically for producing the desired modulation of the control track.

Fig. 6 illustrates a system suitable for the reproduction of the records of the film l0 shown in Fig. 1. This system comprises a control channel and a signal channel as indicated by the legends. The various features of the signal channel may be of any suitable or customary type. They include an exciter lamp I3, the usual sound reproducer optical system M, a photoelectric device 15 arranged to receive light modulated by the sound track of the film I0, an amplifier I6 which amplifies the photoelectric device output and a loudspeaker I! which receives the amplifier output. Also connected to a control circuit of the amplifier I6 is the output of the control circuit.

This control circuit includes an exciter lamp (8, a plate I9 provided with a relatively large aperture 29, a photoelectric device 2! which is preferably of the barrier layer type, a coupling transformer 22 through Which the output of the photoelectric device 2| is supplied to the input of an amplifier 23, a device 24 for detecting or rectifyin the output of the amplifier 23 and a filter network 25 through which the detected amplifier output is supplied to a control-circuit of the main amplifier I6.

As explained in the aforesaid copending application, the amplifier l 6 may include a multi-grid tube having one control grid to which the output of the device I5 is supplied and another control grid to which the detected and filtered output of the device 2| is supplied. Under these conditions, the volume or another characteristic of the reproduced sound may be regulated or controlled in accordance with variation in the control circuit output. The type of control circuit provided for the amplifier IE is, of course, dependent on the function to be regulated by the control circuit. If the frequency range of the reproduced sound is the main consideration, a type of circuit different from that required for volume control must be provided. These various types of control circuit, however, are well known to those skilled in the'art and detailed description of them here would unduly complicate an understanding of the present invention which is applicable to various types of control circuit responsive to a variation in potential or current.

Since the aperture 20 is relatively large and the photoelectric device 2| is subjected to relatively low frequency impulses, the control circuit is highly eilicient and relatively inexpensive. The discontinuous control track is, of course, advantageous from the viewpoint of simplicity and inexpensiveness of the recording apparatus required to produce it.

I claim as my invention:

1. The method which includes exposing successive constant width areas of a sound motion picture film at a frequency dependent on the spacing between periodic discontinuities in said film, varying only the length of said areas in the direction of movement of said film, a point on any one of said areas being equally spaced from similar points on adjacent areas regardless of the lengths of said adjacent areas, and utilizing the variations in the length of said areas to regulate a characteristic of the sound reproduced from said film.

2. The method which includes exposing successive constant width areas of a sound motion picture film at a frequency dependent on the spacing between successive discontinuities in said film, varying only the length of said areas in the direction of movement of said film, a point on any one of said areas being equally spaced from similar points on adjacent areas regardlesss of the lengths of said adjacent areas, and utilizing the variations in the length of said areas to reglate the volume of the sound reproduced from said film.

3. A photographic record including successive surface discontinuities, and exposed constant width areas spaced from one another at a distance dependent on the spacing of said discontinuities and varied in length in the direction of movement of said surface in accordance with the recorded intelligence, a point on any one of said areas being equally spaced from similar points on adjacent areas regardless of the lengths of said adjacent areas.

4. The method which includes exposing successive areas of a photographic record at a frequency dependent upon the spacing between periodic discontinuities of said record, varying the size of said exposed areas in accordance with the recorded intelligence while maintaining similar points on successive areas equidistant from each other, utilizing the periodic discontinuities to produce a carrier current of a frequency determined by the distance between said points for transmitting said recorded intelligence, said variations in size producing a phase modulation of said carrier current, and detecting said carrier frequency to obtain a current coresponding to the variations in size of said areas.

5. The method which includes exposing successive areas of a photographic record at a frequency dependent upon the spacing between periodic discontinuities of said record, varying the size of said exposed areas in accordance with the recorded intelligence while maintaining similar points on successive areas equidistant from each other, utilizing the periodic occurrence of said discontinuities to produce a carrier current having a frequency dependent on the distance between said points, said variations in size phasemodulating said carrier current, and detecting said carrier frequency to produce a current corresponding to the variations in size of said'areas.

6. The method of recording on a record material comprising recording a signal as variations in size of a series of periodic exposed areas on said material, while maintaining similar points on successive exposed areas equidistant from each other to produce a carrier frequency by the periodic occurrences of said areas, said variations in size phase-modulating said carrier frequency, and detecting said carrier frequencies to produce a current corresponding to the variations in size of said areas.

'7. A signal record comprising a periodic series of discontinuities of different sizes and having a point on any one of said discontinuitiesequidistant from similar points on adjacent discontinuities regardless of the sizes of adjacent discontinuities, the periodic occurrence of the discontinuities being adapted to produce a carrier current of constant fundamental frequency but varying in phase in accordance with the variation in sizes of said discontinuities.

8. The method which includes exposing successive areas of a photographic record at a periodicity whereby a point on any one of said areas is equidistant from similar points on adjacent unit areas, said areas being adapted to produce a carrier current of a certain constant fundamental frequency determined by the fixed distance between said points, and varying the length of said areas to produce a phase modulation of said carrier current.

9. The method of claim 8 in which said carrier current is detected and filtered, said'detection producing a current corresponding in amplitude to the variation in length of said areas.

10. The method of claim 8 which includes the step of recording a photographic sound record, the step of detecting said carrier current to produce a current corresponding in variation to the variations in length of said areas, the step of reproducing said sound record, and the step of controlling the amplitude of said reproduction by said detected current.

11. A photographic control record having a series of areas varying in size, any point on one area being equidistant from similar points on adjacent areas and adapted to produce a carrier current of a constant fundamental frequency depending on the spacing between said similar points, said current having an amplitude varying in harmonic frequencies in accordance with the variations in size of said areas.

CHARLES M. BURRILL. 

